Kelly Hoggan, who had served as TSA assistant administrator for security operations since May 2013, was replaced by his deputy, Darby LaJoye, according to the memo from agency head Peter Neffenger.

Long security lines at US airports this spring have frustrated travelers and caused thousands of passengers to miss flights. The TSA has blamed the problem on a lack of security screeners and an increase in passenger volume.

Hoggan came under fire at a US House Oversight Committee hearing on May 12 for receiving more than $90,000 in bonuses and awards over a 13-month period in 2013-14.

Earlier this month, the TSA said it would add more screeners at the country’s busiest airports.

In the memo, Neffenger said the TSA is doing a better job of moving passengers through security at Chicago’s O’Hare Airport after particularly long lines made national news several weeks ago.